1. Field of the Invention
The present invention relates to a pattern formation method for forming a linear pattern by depositing droplets of curable ink by using an inkjet method.
2. Description of the Related Art
As a method for forming a pattern on a substrate, a method for forming a pattern having the thickness of layers deposited on the substrate has been proposed. In the method, curable ink (hereinafter, simply referred to as “ink”) is dropped (for example, ejected) onto the substrate by using an inkjet method in such a manner to form a predetermined pattern, and the ink landed on the substrate is cured to form a layer of cured ink. Further, ink is dropped onto the formed layer of ink, and the ink landed on the layer of ink is cured to form another layer. This operation is repeated to deposit layers of ink.
For example, a method for depositing UV (ultraviolet ray) curable ink on a smooth-surface member is proposed (please refer to Japanese Unexamined Patent Publication No. 2005-205670). In the method, the UV curable ink is ejected from an inkjet head to the smooth-surface member, which is a base plane, and an ultraviolet beam is output from a laser head to the ejected UV curable ink to cure the UV curable ink. Further, each of the inkjet head, the laser head and the smooth-surface member is moved to deposit layers of UV curable ink on the smooth-surface member. Further, a feature that the thickness of a layer is adjusted by controlling a distance between the inkjet head and the laser head is described. By controlling the distance, a time period from ejection of the UV curable ink to the start of radiation of a laser beam is adjusted, and the degree of spreading of the ink is adjusted. Consequently, the thickness of the layer is adjusted.
Further, a method that can prevent clogging of the outlets of nozzles and form a linear pattern with a high aspect ratio without losing the close-contact characteristic has been proposed (please refer to Japanese Unexamined Patent Publication No. 2005-066530). In the method, tiny droplets of liquid are output from the outlets of nozzles at predetermined cycle, and the ejected tiny droplets of liquid are irradiated with pulse light beams. The pulse light beams are output in a time period from time immediately after the tiny droplets of liquid are ejected to time immediately after the tiny droplets of liquid reach the substrate. However, within the period, the pulse light beams are not output in a time period from time immediately before other tiny droplets of liquid are ejected from the outlets of the nozzles to time immediately after the other tiny droplets of liquid are ejected.
Further, a method for forming a spacer that regulates a distance between a pair of substrates is proposed (please refer to Japanese Unexamined Patent Publication No. 2001-083528). The spacer is formed by applying, a plurality of times, a spacer formation material to the same position on the substrate and by curing the applied spacer formation material. Further, a feature that the spacer that has a required height can be more easily formed by reducing the amount of the spacer formation material applied in the second or later application process than that of the spacer formation material applied in the first application process is described.
Here, in the method of forming a three-dimensional pattern by depositing layers of ink by using an inkjet method, when ink lands onto cured ink, the landed ink may spread depending on the properties of the ink (for example, wettability). The landed ink may spread beyond the cured ink under the landed ink (leak from the area of the cured ink under the landed ink to the outside of the area).
To solve this problem, Japanese Unexamined Patent publication No. 2005-205670 adjusts the degree of spreading of wet ink by controlling the time period from landing of the ink to output of a laser beam. When the ink is cured within a predetermined time period after landing, it is possible to prevent the wet ink from spreading. Further, when the ink is cured immediately after landing, it is possible to form a thick layer, in other words, it is possible to cure the landed ink in a high aspect ratio state.
Further, in the method disclosed in Japanese Unexamined Patent Publication No. 2005-066530, flying ink that has been ejected from the nozzles is irradiated with a pulse light beam to make the ink start curing while dropping. In the method, the ink lands onto the substrate after the viscosity of the ink is increased. Therefore, it is possible to cure the ink in a high aspect ratio state.
However, in the method disclosed in Japanese Unexamined Patent Publication No. 2005-205670, the landed ink must be irradiated with a laser beam within a predetermined short period after landing to prevent the wet ink from spreading. Further, in the method disclosed in Japanese Unexamined Patent Publication No. 2005-066530, the ink must be irradiated with light in a time period from time of ejection to time immediately after landing. Therefore, it is necessary that the inkjet head and a light radiation means are arranged in close proximity to each other. Consequently, there is a problem that the flexibility of the apparatus and method becomes lower. In the method disclosed in Japanese Unexamined Patent Publication No. 2005-066530, light for curing the ink is output from a position in the proximity of the inkjet head. Therefore, even if the radiation timing is adjusted, clogging of the nozzles tends to occur by repeated exposure. Consequently, the productivity of the pattern becomes lower.
Further, in the method disclosed in Japanese Unexamined Patent Publication No. 2001-083528, it is possible to prevent the wet ink from spreading by gradually reducing the amount of ink ejected. However, the thickness of a pattern formed by using the method is limited. Further, since the amount of ink is gradually reduced, when a thick pattern is formed, the ink must be ejected many times. Therefore, there is a problem that the productivity of the pattern becomes lower.